OF THE WHITE RIVER BEDS OF MONTANA. 



261 



middle transverse plane of the orbits, and tlieinion. Inward and backward from this are 

 two convexities, one on each side; of the higher part of the sagittal crest. The parieto- 

 temporal suture makes a sigmoid curve upward and backward over the greater convexity 

 of the brain-case and then extends backward parallel with the sagittal crest. 



The interparietal is perfectly distinct from the other bones, having a well-defined 

 suture all around. It is an equilateral triangle. The anterior angle is wedged in between 

 the narrow, forked posterior processes of the parietals. It does not extend quite back to 

 the posterior part of the skull, a narrow border of the supraoccipital intervening. The 

 larabdoid ridges are low, not extending into wings. 



The supraoccipital is nearly as broad as high. It is more nearly Hat than in Oreo- 

 don, culbertsoni or 0. gracilis. Above it is slightly concave, with a hint of a median 

 ridge. Below it is broadly convex and almost flat above the foramen magnum. 



The basioccipital is narrow and sharply angulate below, the angular portion being in 

 the same plane as the palate. 



The tympanic bulla 1 are near together, Large, high, evenly rounded, elliptical in out- 

 line, as seen from below, with the. longer axis antero-posterior ; and they project downward 

 farther than any other elements of the skull.* They are proportionally larger than in 

 Eporeodon (Princeton Col., No. 10586). The external auditory meatus is trumpet- 

 shaped like that of Oreodon culbertsoni, and it fills the space between the exoccipital and 

 the post-glenoid process. The foramen ovale is above the anterior portion of the tympanic 

 bulla. The foramen rotundum is small and just outside the posterior beginning of the 

 pterygoids. 



The posterior nares open between the anterior lobes of the last molars. The poster- 

 ior median portions of the palatines end in a blunt point. The palate is concave in a 

 transverse line and narrow. The posterior palatine foramina are between the interval 

 between the last premolars and first molars. 



The glenoid surface is somewhat convex antero-posteriorly, about the same as in 

 Oreodon culbertsoni. The post-glenoid processes are broad transversely, bounding the 

 whole glenoid surface posteriorly and extending out-ward nearly as far as the maximum 

 expansion of the zygomatic arches, which is just anterior to the glenoid surface. 



As before stated, the skull is very nearly the size of that of Oreodon gracilis. Its 

 likeness to that seems more apparent on hasty examination than after detailed study. In 

 many respects, as in the flatness of the top of the skull, the large size and superior posi- 

 tion of the orbits, the shape of the brain-case and the size and form of the; tympanic bulhe, 

 it more; resembles Eporeodon (?). In a specimen of this genus (Princeton Coll., No. 

 10568) which I have used tor comparison, the postorbital processes of the frontal and 



* Probably the parocclpital processes extended lower, but they are broken oil'. 



A. 1>. S. — VOL. XX. HH. 



